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Showing papers by "University of Chicago published in 1973"


Journal ArticleDOI
01 Jun 1973-Nature
TL;DR: An unsuspected abnormality in all cells from the nine patients with chronic myelogenous leukaemia has been detected with quinacrine fluorescence and various Giemsa staining techniques, suggesting that there may be a hitherto undetected translocation between the long arm of 22 and thelong arm of 9, producing the 9q+ chromosome.
Abstract: CELLS from nine consecutive patients with chronic myelogenous leukaemia (CML) have been analysed with quinacrine fluorescence and various Giemsa staining techniques. The Philadelphia (Ph1) chromosome in all nine patients represents a deletion of the long arm of chromosome 22 (22q−)1,2. An unsuspected abnormality in all cells from the nine patients has been detected with these new staining techniques. It consists of the addition of dully fluorescing material to the end of the long arm of one chromosome 9 (9q+). In Giemsa-stained preparations, this material appears as an additional faint terminal band in one chromosome 9. The amount of additional material is approximately equal to the amount missing from the Ph1 (22q−) chromosome, suggesting that there may be a hitherto undetected translocation between the long arm of 22 and the long arm of 9, producing the 9q+ chromosome.

4,103 citations


Journal ArticleDOI
TL;DR: It is shown that this particular mode reproduces some of the phenomenology of visual psychophysics, including spatial modulation transfer function determinations, certain metacontrast effects, and the spatial hysteresis phenomenon found in stereopsis.
Abstract: It is proposed that distinct anatomical regions of cerebral cortex and of thalamic nuclei are functionally two-dimensional. On this view, the third (radial) dimension of cortical and thalamic structures is associated with a redundancy of circuits and functions so that reliable signal processing obtains in the presence of noisy or ambiguous stimuli. A mathematical model of simple cortical and thalamic nervous tissue is consequently developed, comprising two types of neurons (excitatory and inhibitory), homogeneously distributed in planar sheets, and interacting by way of recurrent lateral connexions. Following a discussion of certain anatomical and physiological restrictions on such interactions, numerical solutions of the relevant non-linear integro-differential equations are obtained. The results fall conveniently into three categories, each of which is postulated to correspond to a distinct type of tissue: sensory neo-cortex, archior prefrontal cortex, and thalamus. The different categories of solution are referred to as dynamical modes. The mode appropriate to thalamus involves a variety of non-linear oscillatory phenomena. That appropriate to archior prefrontal cortex is defined by the existence of spatially inhomogeneous stable steady states which retain contour information about prior stimuli. Finally, the mode appropriate to sensory neo-cortex involves active transient responses. It is shown that this particular mode reproduces some of the phenomenology of visual psychophysics, including spatial modulation transfer function determinations, certain metacontrast effects, and the spatial hysteresis phenomenon found in stereopsis.

1,796 citations


Journal ArticleDOI
TL;DR: In this article, the authors apply economic theory to an analysis of behavior in the public sector, focusing on the division of interest between the public and its political representatives, where the public officeholder is assumed to act to advance his own interests, and these interests do not coincide automatically with those of his constituents.
Abstract: This paper applies economic theory to an analysis of behavior in the public sector. The model focuses on the division of interest between the public and its political representatives. The division of interest arises because the public officeholder is assumed to act to advance his own interests, and these interests do not coincide automatically with those of his constituents. The electoral process and some elements of the political structure are then analyzed as mechanisms which can be used to move the officeholder toward a position where the advancement of self-interest approximates the advancement of the interests of his constituents.

1,473 citations


Journal ArticleDOI
01 May 1973-Genetics
TL;DR: Using data from human populations, this work has shown highly significant heterogeneity in F values for human polymorphic genes over the world, thus demonstrating that a significant fraction of human polymorphisms owe their current gene frequencies to the action of natural selection.
Abstract: The variation in gene frequency among populations or between generations within a population is a result of breeding structure and selection. But breeding structure should affect all loci and alleles in the same way. If there is significant heterogeneity between loci in their apparent inbreeding coefficients F=s(p) (2)/p(1-p), this heterogeneity may be taken as evidence for selection. We have given the statistical properties of F and shown how tests of heterogeneity can be made. Using data from human populations we have shown highly significant heterogeneity in F values for human polymorphic genes over the world, thus demonstrating that a significant fraction of human polymorphisms owe their current gene frequencies to the action of natural selection. We have also applied the method to temporal variation within a population for data on Dacus oleae and have found no significant evidence of selection.

1,216 citations


Journal ArticleDOI
TL;DR: A mapping to study the qualitative properties of continuous biochemical control networks which are invariant to the parameters used to describe the networks but depend only on the logical structure of the networks.

1,016 citations


Journal ArticleDOI
TL;DR: In this article, a generalization of classical Hamiltonian dynamics to a three-dimensional phase space is proposed, where the equation of motion involves two Hamiltonians and three canonical variables.
Abstract: Taking the Liouville theorem as a guiding principle, we propose a possible generalization of classical Hamiltonian dynamics to a three-dimensional phase space. The equation of motion involves two Hamiltonians and three canonical variables. The fact that the Euler equations for a rotator can be cast into this form suggests the potential usefulness of the formalism. In this article we study its general properties and the problem of quantization.

1,007 citations


Journal ArticleDOI
TL;DR: In this paper, a general formalism for a system whose Hamiltonian is periodic in time is presented for the interactions between bond electrons and an external electromagnetic field, which can be treated semiclassically, such as electric and magnetic polarizations, optical rotation, and transitions among discrete levels.
Abstract: A general formalism is presented for a system whose Hamiltonian is periodic in time The formalism is intended to deal with the interactions between bond electrons and an external electromagnetic field, which can be treated semiclassically, such as electric and magnetic polarizations, optical rotation, and transitions among discrete levels A particular bound-state solution of the Schr\"odinger equation which belongs to an irreducible representation of the time-translation symmetry group is defined as a steady state, and the characteristic number of the irreducible representation as a quasienergy It is shown that the defined steady states and quasienergies behave in a newly constructed Hilbert space like stationary states and energies of a conservative system in many respects It is also shown that for a resonant case the unperturbed quasienergy becomes degenerate and the transitions among discrete levels can be accounted for by the familiar degenerate perturbation procedure Using a suitable Hilbert space, the steady states are established as firmly as the stationary states stand in the theory of a conservative system

902 citations


Journal ArticleDOI
01 Dec 1973-Genetics
TL;DR: There is a characteristic length scale of variation of gene frequencies, (see PDF) and the population cannot respond to changes in environmental conditions which occur over a distance less than the characteristic length.
Abstract: A model of the effect of gene flow and natural selection in a continuously distributed, infinite population is developed. Different patterns of spatial variation in selective pressures are considered, including a step change in the environment, a "pocket" in the environment and a periodically varying environment. Also, the problem of the effect of a geographic barrier to dispersal is analyzed. The results are: (1) there is a characteristic length scale of variation of gene frequencies, (see PDF). The population cannot respond to changes in environmental conditions which occur over a distance less than the characteristic length. The result does not depend either on the pattern of variation in selective pressures or on the exact shape of the dispersal function. (2) The reduction in the fitness of the heterozygote causes a cline in gene frequencies to become steeper. (3) A geographic barrier to dispersal causes a drastic change in the gene frequencies at the barrier only when almost all of the individuals trying to cross the barrier are stopped.

736 citations


Journal ArticleDOI
02 Nov 1973-Science
TL;DR: The oxygen of anhydrous, high-temperature minerals in carbonaceous meteorites is strongly depleted in the heavy stable isotopes 17O and 18O and probably results from the admixture of a component of almost pure 16O.
Abstract: Oxygen isotope analysis of anhydrous high-temperature phases from carbonaceous meteorite chondrites indicates a high degree of O(17) and O(18) isotope depletion. The isotope decay is believed to be a result of nuclear rather than chemical processes caused by the admixture of a component consisting of almost pure O(16). It is theorized that this component may predate the solar system and may represent interstellar dust with a separate history of nucleosynthesis.

735 citations


Journal ArticleDOI
12 Oct 1973-Science
TL;DR: It is proposed that receptor transformation is an important step in estrogen action and that a principal role of the hormone is to induce conversion of the receptor protein to a biochemically functional form.
Abstract: The interaction of estradiol with uterine cells involves the association of the hormone with an extranuclear receptor protein, followed by temperature dependent translocation of the resulting complex to the nucleus. During this process, the steroid binding unit of the protein undergoes an alteration, called "receptor transformation," that can be recognized by an increase in its sedimentation rate from 3.8S to 5.2S, and by its acquisition of the ability to bind to isolated uterine nuclei and to alleviate a tissue specific deficiency in the RNA synthesizing capacity of such nuclei. Receptor transformation can be effected in the absence of nuclei by warming uterine cytosol with estradiol. This preparation of transformed complex resembles that extracted from nuclei both in its sedimentation rate (5.3S) and in its ability to bind to uterine nuclei and augment RNA synthesis, properties that are not shown by the native complex. It is proposed that receptor transformation is an important step in estrogen action and that a principal role of the hormone is to induce conversion of the receptor protein to a biochemically functional form.

709 citations


Journal ArticleDOI
TL;DR: In this paper, a new formulation for the angular distribution and the polarization of light excited by atomic and electronic collisions and modulated in time by the action of internal and external fields is presented.
Abstract: A new formulation is presented for the angular distribution and the polarization of light excited by atomic and electronic collisions and modulated in time by the action of internal and external fields. The formulation disentangles geometrical and dynamical effects and stresses the extraction of data on the alignment and orientation of radiating atoms from observations of the emitted light. The treatment is set in the context of recent experimental and theoretical literature and points to new avenues of research.

Journal ArticleDOI
TL;DR: Treatment of isolated human erythrocyte membranes with Triton X-100 at ionic strength ⋍0.04 preferentially released all the glycerolipid and glycoprotein species and the polypeptide elution profile obtained with nonionic detergents is nearly reciprocal to that previously seen with a variety of agents which perturb proteins.
Abstract: Treatment of isolated human erythrocyte membranes with Triton X-100 at ionic strength ⋍0.04 preferentially released all the glycerolipid and glycoprotein species. At low ionic strength, certain nonglycosylated polypeptides were also selectively solubilized. The liberated polypeptides were free of lipids, but some behaved as if associated into specific oligomeric complexes. Each detergent-insoluble ghost residue appeared by electron microscopy to be a filamentous reticulum with adherent lipoid sheets and vesicles. The residues contained most of the membrane sphingolipids and the nonglycosylated proteins. The polypeptide elution profile obtained with nonionic detergents is therefore nearly reciprocal to that previously seen with a variety of agents which perturb proteins. These data afford further evidence that the externally-oriented glycoproteins penetrate the membrane core where they are anchored hydrophobically, whereas the nonglycosylated polypeptides are, in general, bound by polar associations at the inner membrane surface. The filamentous meshwork of inner surface polypeptides may constitute a discrete, self-associated continuum which provides rather than derives structural support from the membrance.

Journal ArticleDOI
TL;DR: The distinctive elution behavior which defines these two groups of polypeptides relates both to their chemical composition and their organizational disposition in the membrane.
Abstract: Isolated human erythrocyte membranes were exposed to a series of reagents known to modify or perturb proteins; these included sodium hydroxide, lithium diiodosalicylate, acid anhydrides, and organic mercurials. Each reagent liberated the same set of relatively polar polypeptides from the membrane, while the other, more hydrophobic species invariably remained associated with the membrane residue. The selective elution pattern was precisely that seen previously with 6 M guanidine hydrocloride. The released polypeptides, comprising half of the membrane protein mass, contained no carbohydrate; current evidence indicates that all of these components are confined to the cytoplasmic surface of the membrane. The residue contained all the lipids and all the glycoproteins. The latter are accessible to the outer membrane surface and, in at least two cases, seem to extend asymmetrically across the thickness of the membrane. Thus, the distinctive elution behavior which defines these two groups of polypeptides relates both to their chemical composition and their organizational disposition in the membrane.

Journal ArticleDOI
TL;DR: In this paper, a positive economic theory of the legal system is presented, and the authors attempt to explain the procedural rules and practices that give the system its distinctive structure and to predict the effects of changes in one part of the system on the other parts.
Abstract: requires an understanding of the operating principles of the system for resolving legal disputes. This article seeks to advance that understanding by means of the powerful tools of economic theory. Although it builds on recent articles by William M. Landes and by the present writer,' it is more than an extension of the previous work. That work took for granted the rules of procedure that provide the framework of the legal dispute-resolution system; the emphasis was on how plaintiffs (mainly prosecutors) and defendants maximize utility within its constraints. The present article attempts to explain the procedural rules and practices that give the system its distinctive structure and to predict the effects of changes in one part of the system on the other parts. It thus adds to the literature (as yet small) that is developing a positive economic theory of the institutions of the legal system.2 Part I explains the basic analytical framework of the article. The purpose of

Journal ArticleDOI
TL;DR: The topography of the median eminence-pituitary catecholamine innervation has been studied with respect to the origin, course and termination of its different components.


Journal ArticleDOI
TL;DR: A simple model of the effects of time on memory is described, where the effect of forgetting and telescoping where the event is remembered as occurring more recently than it did is combined.
Abstract: This article describes a simple model of the effects of time on memory. The model combines the effects of forgetting and telescoping where the event is remembered as occurring more recently than it did. The model is tested on behavior data for which validation information are available. The use of records and of aided recall are shown to have opposite effects on memory errors. Records reduce telescoping effects, but not errors of omission. Aided recall reduces omissions, but does not reduce and may even increase telescoping. The article also includes a discussion of other characteristics of the interview and the respondent that affect memory.

Journal ArticleDOI
TL;DR: Application of mathematical techniques to the study of experimental left ventricular hypertrophy and thyroxin-stimulated growth of myocardial cells has confirmed and extended the results of quantitative measurements on electron micrographs, suggesting that the approaches described can form the basis of a quantitative electron microscopic and microchemical pathology of heart muscle.
Abstract: Mathematical techniques can be used to extract quantitative information from tissue electron micrographs of heart muscle With these methods it has been possible to measure the fractions of myocardial cell volume made up of myofibrils, mitochondria, sarcotubules, T system and sarcoplasm, as well as the membrane areas per unit of cell volume of plasma membrane, sarcotubular membrane and mitochondrial cristae The techniques have been used to quantitate the changes in the ultrastructure of myocardial cells in experimental left ventricular hypertrophy and in experimentally induced hypothyroidism before and after treatment with thyroxin These measurements have demonstrated striking and physiologically significant changes in the ultrastructural composition of the cells The pattern of ultrastructural change in ventricular hypertrophy differs in characteristic ways from the pattern during thyroxin-stimulated cardiac cellular growth These observations have suggested certain generalizations about the constraints to which growing myocardial cells are subject New and simple microchemical methods have been developed to determine the cardiac contents of myofibrils and mitochondrial cristae The methods are applicable to samples of heart muscle obtained at autopsy, surgery or biopsy, as well as to experimental material Application of these techniques to the study of experimental left ventricular hypertrophy and thyroxin-stimulated growth of myocardial cells has confirmed and extended the results of quantitative measurements on electron micrographs It is suggested that the approaches described can form the basis of a quantitative electron microscopic and microchemical pathology of heart muscle

Journal ArticleDOI
TL;DR: Analyses of polypeptides made in HEp-2 cells infected with herpes simplex virus type 1 by high-resolution polyacrylamide gel electrophoresis revealed the synthesis of at least 49 infected cell polypePTides (ICP), which can account for 75% of the virus genetic information assuming a DNA molecular weight of 10(8) and asymmetric transcription.
Abstract: Analyses of polypeptides made in HEp-2 cells infected with herpes simplex virus type 1 by high-resolution polyacrylamide gel electrophoresis revealed the synthesis of at least 49 infected cell polypeptides (ICP) ranging in molecular weight from 15,000 to 280,000. Evidence for virus specificity based on increased rates of synthesis postinfection, immunological specificity, and viral control of mobility and rate of synthesis was available for 47 of the ICP. These 47 polypeptides can account for 75% of the virus genetic information assuming a DNA molecular weight of 10(8) and asymmetric transcription. On the basis of their mobility relative to virion proteins, the ICP were classified as structural (S, 23 polypeptides), nonstructural (NS, 16 polypeptides), and unassigned (U, 10 polypeptides). Analysis of the synthesis of the ICP revealed the following. (i) Rapid posttranslational cleavages of HSV proteins were not detected; in parallel experiments rapid posttranslational cleavages were readily demonstrated in poliovirus-infected cells and these were blocked by protease inhibitors. (ii) Slow posttranslational changes in the mobility of at least two polypeptides were observed. (iii) Analysis of the rates of synthesis of ICP examined at four intervals postinfection revealed regulation of the pattern and amount of ICP synthesized. ICP formed six classes (A to F) differing in their kinetics of synthesis. S and NS ICP were distributed nonrandomly among these classes. Thus, of the sum of S protein amino acid sequences apportioned among these kinetic classes, 47%, constituting class A and comprising "late" structural proteins, were characterized by progressively increasing rates of synthesis until at least 12 h postinfection; whereas "early" structural proteins constituting class C, amounting to 31% of the total amino acid sequences, were synthesized with initially increasing rates until 4 h postinfection and with declining rates thereafter. NS polypeptides and remaining S polypeptides were distributed among the other kinetic classes-B, D, E, and F. Control of protein abundance was evident in that the polypeptides were not made in equimolar amounts. However, S and NS polypeptides could not be differentiated on the basis of their molar rates of synthesis. The bulk of the detected polypeptides did not differ by more than eightfold in their molar rates of synthesis.

Journal ArticleDOI
TL;DR: The first high temperature superconducting oxide compound is Li1+xTi2−xO4 and has the face-centered cubic spinel structure, with a o ≊ 8.40 A.

Journal ArticleDOI
TL;DR: The inability of ventricular myocardial cells to regenerate stands in sharp contrast to skeletal muscle, which is capable of considerable tissue repair, involving both regeneration of individual fibers and reconstitution of the whole muscle.
Abstract: During the embryonic development of the myocardium both undifferentiated cells and cells containing muscle-specific proteins divide. As the heart grows and approaches maturity, its muscle cells progressively lose their mitotic activity; myocardial cell enlargement then becomes the principal process by which the heart as a whole enlarges. Mitotic figures in nuclei of heart muscle cells are frequent in the neonatal rat but become very rare at about the third month of postnatal life. Both in the developing and adult animal the work load is one of the determinants of cardiac size. The cytologic features of cardiac enlargement depend on the stage of development of the heart at the time when the stimulus to growth occurs. A work load imposed on embryonic or early neonatal hearts results in enlargement characterized by an increase in both the number and size of myocardial cells. The adult heart enlarges only by enlargement of its component muscle cells. Division of ventricular muscle cells in mammals is not activated after cardiac injury. The inability of ventricular myocardial cells to regenerate stands in sharp contrast to skeletal muscle, which is capable of considerable tissue repair, involving both regeneration of individual fibers and reconstitution of the whole muscle.

Book
01 Jan 1973
TL;DR: Widowhood in an American City as discussed by the authors examines the roles and lifestyles of urban American widows fifty years of age or older and argues that the way women reengage society following the death of a husband is different due to their location in the modern social system.
Abstract: Widowhood in an American City focuses on the roles and lifestyles of urban American widows fifty years of age or older. These women form a segment of two generations of one society; they present a historical instance of people born and brought up under conditions that are not likely to be duplicated. Not only the U.S., but many other countries are undergoing modifications in the degrees and forms of urbanization, industrialization, and social complexity.Helena Znaniecki Lopata argues that the way women re-engage society following the death of a husband is different due to their location in the modern social system. She notes that the trends in social structure are toward increasingly voluntaristic engagement in achieved, functionally oriented social roles that are performed in large groups and contain secondary social relations. The cultural background of many societal members prevents the utilization of most resources of the complex urban world, restricting them to a small social life space, with almost automatically prescribed social relations.Those who argue that the elderly are socially isolated contend that this is a result of the natural process of withdrawal of the person and the society from each other. These arguments focus on those who are isolated or lonely and those who lack the skills, money, health, and transportation for engaging or re-engaging society. Lopata's study indicates that this assumption is false for many widows. If such people are to be helped, a fresh view of the relation between the urban, industrial, and complex modern world and its residents is required, and new action programs must be creatively developed. This is a timely, ground-breaking work that addresses and shatters common myths associated with growing old alone in an urban society.

Journal ArticleDOI
TL;DR: Rhesus monkeys were trained on a fixed-interval 9-min limited-hold 3-min schedule of intravenous cocaine reinforcement, and response rate for cocaine reinforcement was shown to be a positive function of reinforcement magnitude for a dose range from 0 to 800 ug/kg/inj.
Abstract: Rhesus monkeys were trained on a fixed-interval 9-min limited-hold 3-min schedule of intravenous cocaine reinforcement. A 15-min timeout followed each reinforcement or limited-hold expiration. An identical schedule of food reinforcement was interspersed in the session to assess rate-modifying effects of the drug infusions not specific to drug reinforcement. In one experiment, response rate for cocaine reinforcement was shown to be a positive function of reinforcement magnitude for a dose range from 0 to 800 ug/kg/inj. At these doses, there was little effect on food reinforced responding except at the highest dose, where responding decreased. Results of the second experiment indicated that increasing the duration of the cocaine infusion produced a change in response rate similar to decreasing unit dose. The response rate change for a given increase in infustion duration was less at a unit dose of 400 ug/kg than at 200 ug/kg.

Journal ArticleDOI
TL;DR: In this article, it was shown that a system of cells which are attracted by chemotaxis to a signal released by themselves can aggregate (in the form of delta function concentrations).

Journal ArticleDOI
TL;DR: An algorithm for solving resource-constrained network scheduling problems, a general class of problems that includes the classical job-shop-scheduling problem, that uses Lagrange multipliers to dualize the resource constraints, forming a Lagrangian problem.
Abstract: This paper presents an algorithm for solving resource-constrained network scheduling problems, a general class of problems that includes the classical job-shop-scheduling problem. It uses Lagrange multipliers to dualize the resource constraints, forming a Lagrangian problem in which the network constraints appear explicitly, while the resource constraints appear only in the Lagrangian function. Because the network constraints do not interact among jobs, the problem of minimizing the Lagrangian decomposes into a subproblem for each job. Algorithms are presented for solving these subproblems. Minimizing the Lagrangian with fixed multiplier values yields a lower bound on the cost of an optimal solution to the scheduling problem. The paper gives procedures for adjusting the multipliers iteratively to obtain strong bounds, and it develops a branch-and-bound algorithm that uses these bounds in the solution of the scheduling problem. Computational experience with this algorithm is discussed.

Journal ArticleDOI
TL;DR: It is found that many potent synthetic androgens can bind directly to β protein and to prostate cell nuclei without a metabolic conversion, indicating that the bulkiness and flatness of the steroid molecule play a more important role in receptor binding than the detailed electronic structure at the Δ4 bond of Ring A.

Book ChapterDOI
01 Jan 1973
TL;DR: In this paper, the life cycle is viewed from each of three dimensions of time: life time (or chronological age), historical time, and social time, or the system of age grading and age expectations which shapes the life-cycle.
Abstract: Students of the life cycle have given much attention to the biological timetable of human development, but much less attention to the socio-historical context. A few of the major sociological concepts significant for understanding personality are briefly reviewed–namely, social system, social role, and socialization, and each is discussed in relation to a time dimension in looking at the life course. The life cycle is then viewed from each of three dimensions of time: life time (or chronological age); historical time; and social time, or the system of age grading and age expectations which shapes the life cycle. After a brief discussion of age norms as a system of social control, and of age stratification in society, there follows a description of the changing rhythm of the life cycle in American society, illustrating how historical time, social time, and life time are intertwined.

Journal ArticleDOI
TL;DR: In this paper, Carleson and Sjolin gave a new proof of a theorem of L. Carleon and P.Sjolin on the boundedness of spherical summation operators in two variables.
Abstract: We give a new proof of a theorem of L. Carleson and P. Sjolin onL p -boundedness of spherical summation operators in two variables.

Journal ArticleDOI
TL;DR: It is hypothesized that a fraction of erythrocyte glyceraldehyde-3-P dehydrogenase may be specifically bound to the inner surface of the membrane in vivo in a fashion which is responsive to metabolic and ionic transients.

Journal ArticleDOI
TL;DR: The performance and reliability of amorphous semiconductor devices that deal with the handling of information in the form of switching, modulation, storage, and display are discussed in this article.
Abstract: Performance and reliability of amorphous semiconductor devices that deal with the handling of information in the form of switching, modulation, storage, and display are discussed. Structural changes between a disordered and a more ordered state and the concomitant large change in many material properties offer the possibility of using amorphous semiconductors for high-density information storage and high-resolution display devices. The structural changes can be initiated by various forms of energy such as an electrical pulse, a short light pulse, or a brief light exposure. Many materials show good structural reversibility. The sensitivity of an amorphous photostructural film is amplified by several orders of magnitude by first forming a latent image by photonucleation and subsequent dry development by heat or radiation. Examples of optical contrast and resolution in image formation are given. The major differences between crystalline and amorphous semiconductors are briefly outlined.